1. Field of the Invention
The present invention is generally in the field of electrical circuits. More particularly, the invention is in the field of line drivers for transmission lines.
2. Background Art
Line drivers, such as current mode line drivers, can be utilized in set-top boxes, cable modems, routers, computer interfaces, and other electronic devices to drive transmission lines, such as Ethernet transmission lines. For a line driver, such as a current mode line driver, a tail current source can provide a tail current for generating an output signal during line driver operation. The tail current source needs to provide a sufficient amount of tail current to enable the output signal generated by the line driver to reach a desired maximum amplitude. However, it is important to effectively control the amount of tail current provided to the line driver by the tail current source so as to avoid undesirably increasing line driver current consumption.
Conventionally, a tail current source for providing a tail current for a line driver, such as a current mode line driver, can include, for example, a pair of field effect transistors (FETs) coupled in series between a node of the line driver and ground. A bias circuit can be configured to provide a bias voltage at the gate of each FET in response to a pair of bias currents supplied to the bias circuit. By controlling the bias voltages provided at the gates of the FETs by the bias circuit, the tail current provided for the line driver by the conventional tail current source can also be controlled. However, it is difficult for the bias circuit to effectively and accurately control the tail current provided by the conventional tail current source, which can result in an undesirable increase in line driver current consumption.